1. Field of the Invention
The present invention relates to a device for positioning a cutting guide relative to a bone. It applies to orthopaedic surgical procedures such as, for example, joint replacement surgery.
2. Discussion of the Related Art
In joint replacement operations, it is often required that portions of the ends of the bones of the joint be resected and replaced with endoprosthetic implants. In particular, for knee joint replacements, it is very important that the implants be well positioned on and well oriented to each bone, because deviations of 2 mm or 2° can jeopardize the success of the operation.
In order to cut the bones in a specific cutting plane, a surgeon commonly uses a cutting guide which includes a flat or slotted surface for guiding a saw blade in the cutting plane. Some cutting guides allow the guiding of the saw blade in several different cutting planes. For example, some cutting guides define 4, 5 or even 8 cutting planes and are generally called 4-in-1, 5-in-1 and 8-in-1 cutting guides, respectively. Examples of such cutting guides can be found in United States patent U.S. Pat. No. 5,474,559 filed by Zimmer and Dennis W. Burke and entitled “Femoral milling instrumentation for use in total knee arthroplasty with optional cutting guide attachment” and in patent application WO 98 32 384, filed by the New York Society for the Ruptured and Crippled Maintaining the Hospital for Special Surgery and entitled “Method and apparatus for femoral resection”.
The surgeon usually positions a cutting guide relative to a bone by means of a positioning device. There exist several types of device for positioning a cutting guide relative to a bone.
United States patent U.S. Pat. No. 5,562,674, filed by Zimmer and entitled “Intramedullary rod with guide member locator” describes a device for positioning a cutting guide including a intramedullary rod with an adjustment mechanism to position the cutting guide in the correct varus/valgus orientation with respect to the intramedullary canal of the bone.
United States patent U.S. Pat. No. 6,712,824 filed by Aesculap AG & CO KG and entitled “Apparatus for positioning the angle of a bone cutting guide” describes an apparatus for positioning the cutting angle of a bone cutting guide, wherein the bone is a tibia or a femur, which includes a first fastener to fasten the positioning apparatus to the bone such that the whole of the apparatus and the fastener of the cutting guide can rotate relative to the fastening axis, and a second fastener to fasten the positioning apparatus at a second fastening location onto the bone different from the first fastening location, so as to fix the apparatus at a required position within the rotation relative to the first fastening axis.
Computer navigation has been recently introduced into surgery to aid the surgeon in positioning cutting guides accurately relative to the bones. In these devices, marking elements are attached to the bones, and their positions are monitored with a suitable camera. For example, the marking elements are passive light reflecting spheres or disks, or active infrared light or ultrasound emitters. By kinematic movements, or by scanning points on the bones, the navigation system can determine and/or display the optimal position of each implant in a coordinate system associated to the bone, as per a surgical criterion, such as alignment relative to the mechanical axis of the bones.
United States patent U.S. Pat. No. 6,554,837 filed by Plus Endoprothethik and entitled “Device and method for inserting a prosthetic knee” describes a positioning device with a base that attaches to the bone. This positioning device is actuated by motors commanded by a computer.
French patent application FR 03/07340, still not published, filed by PRAXIM and entitled “Dispositif de positionnement de guide de coupe osseuse” describes a 6 degrees of freedom cutting guide positioning device, the position of which is monitored by a localization device.
The main disadvantage of the previously described positioning devices is that they rely on an anchoring member or a base component which must be first fixed to the bone, and a number of positioning elements that connect the cutting guide to the base for adjusting the angle and/or the position of the cutting guide relative to the base with a least 1 and up to 6 degrees of freedom. These types of devices therefore usually take up considerable space in the vicinity of the bone and are invasive for the patient. Moreover, since an anchoring member or a base component is first fixed to the bone, such positioning devices lead to unnecessary damages of the bone. Besides, such positioning devices are usually time consuming to install.